NOT SO FAST, Bill Berson

[Bill Greenwood]

In the long 7 page discussion of AOA indicators, Bill Berson wrote that
"wings stall at less angle with flaps down" and by angle it is clear that he means angle of attack.

I disagreed and thus Bill gave a reference to Langewiesche as his source and specificly tells me to "go to page 166 for the proof and a chart listed as figure 13-2. "

So I did just as he said, and got my copy out, looked at it, and I don't see it. One of us Bill's must have a different version of the book or have a vivid imagination.
First of all there is very little discussion of flaps in the whole book. There is no chapter on flaps, there is only 2 short references for a half page each on page 83 and 256 and neither mention angle of attack at all. He writes, "Flaps have the double purpose of lowering the airplane's stalling speed," etc.

Next the whole chapter of which p166 is part of, is titled The Ailerons, and has no mention of flaps. Yes, it talks about aileron effects on stall, but that is not the part I wrote about or am writing on now. An aileron and a landing flap are not the same thing.

As for proof in the "figure 13-2", once again, it is not in my book, The illustrations are not numbered at all and there is not one that shows a graph for stall speed as higher with flaps down. Mine is copywrited 1944 and renewed 1972.

So Bill Berson, as they say in legal circles, which Bill has the true bill?

Now if anyone wants to comment on this, besides the other Bill, fine, but I'd ask you to keep it on this specific point which is about the affect of FLAPS , (not ailerons) on stall speed and the angle of attack. And my discussion here is only this point , not about if AOA indicators are good or which brand is best, that was the other topic.
Thanks, Bill G

[Bill Berson]

To Bill Greenwood,
The figure 13-2 is in this web link:http://books.google.com/books?id=i8r...0angle&f=false

[Bill Berson]

It's true, The book Stick and Rudder does not have a chapter on flaps. That why I used the aileron as an example.

For more details:
I would also suggest a careful reread of Ron Blum's post #55 here:http://eaaforums.org/showthread.php?...t=Angle+attack

[Bill Greenwood]

Well, Bill, as least we agree with what I wrote, in that page 166 on Langeweiche does not say, and has nothing to do with flaps and stall speed.
I may not be as young as I used to be, but I was the best reader in my elementary school and just went to the FAA Dr. today and passed my eye test at 20-20 with no glasses.
By the way, I was also probably the worst dancer in my school, and I might be the worst computer guy on this forum, but you can't win em all.

Now as for the figure 13-2, and your pages from the Rich Stowell book, well I just don't read it the same way you do. He talks about stall speed and bank angle for instance. Nowhere do I see a straight forward statement that says ,"Flaps make a wing stall at a lower angle of attack", and I am talking just landing flaps down vs clean, nothing about changing g loading or weight or bank angle or ailerons.
If he has that simple phrase somewhere that I missed please quote it.

I have heard Rich speak at EAA, and if I go to his lecture this year, I will ask him that specific question.
I do like his simple PARE spin recovery idea, and it works in the planes I have flown, but I have also heard and even read on this forum that some acro guys dispute it and like to bring up a few airplanes that it may not work on.
I have phoned a couple of current CFI friends. All agree that flaps lower the stall speed, just as I am saying and as Langweiche is saying. But they are not sure when you phrase it only on angle of attack,and they start to hedge their statements. One thinks flaps don't change the stall angle of attack at all, but like me he can't see how they would make it stall at a lower angle.

Just seems to me if a plane with flaps down can fly at a lower airspeed without stalling than when clean, it must indicate that it can fly at a higher angle of attack before stalling than if clean.

I, of course, may be wrong. I once voted for Nixon, and once bought a VW Rabbit and both proved to be defective.

[Matt Gonitzke]

Bill G.-

Go find a copy of Theory of Wing Sections by Abbott and Von Doenhoff and look at the CL vs. AOA graph for any airfoil in it. You'll notice that the CL vs. AOA curve peaks at a lower AOA and higher CL with the deflected flap than the clean configuration.

[Bill Berson]

Thanks Matt,
I just got out my copy of Theory of Wing Sections to find a reference to quote.
You beat me to it.

[Victor Bravo]

In the long 7 page discussion of AOL indicators,

AOL indicators include:
1) receiving hundreds of useless computer disks in the mail weekly,
2) being inundated and besieged with hundreds of offers and purchase opportunities when all you're trying to do is check your e-mail, and
3) being viewed as a little less educated and computer savvy by the rest of the internet world.

AOA indicators, on the other hand, give you information about an airplane wing's angle of attack.

[Bill Greenwood]

Matt, I don't have a copy of the book on wing theory that you refer to, and won't order one just for this.
I did look up the authors info, lot's of credentials but a long time ago.

So I have three questions:

1. Are you saying that the peak of CL which I understand is lift, is where the stall occurs?

2. Since that book is about theory, is there anywhere in the book that refers to a real airplane test in actual flight, and has a simple direct statement to the point that Bill Berson made, which was,
"wings stall at a lower angle with flaps down"

3. If flaps do what you and Bill B say, then why do many airplanes take off with partial flaps? It seems under your way, they would be handicapping themselves and setting the plane up to stall sooner, ie at a lower angle of attack than clean?

I may be dense and of course have not flown with AOA indicators, but rather airspeed indicators for all these years, and I don't read a lot of design or theory books, more of Pilot Notes or flight manuals which tell you the airplane performance, but re airspeed.

Thanks, Bill G.

[Bill Berson]

Bill G.
I think it is important as a pilot, that you understand how a down aileron can initiate a stall.
You seem to refuse to think about ailerons. But from a pure physics point of view, the aileron is virtually the same as the flap.
You need to know this.

[Matt Gonitzke]

Bill G.-

3 answers (hopefully):

1. Yes. Here is a picture of one page of the book for reference:
http://www.boatdesign.net/forums/att...-naca-0012.jpg

2. There are methods to transform a 2D airfoil CL vs. AOA graph into one for a 3D wing that are described in other books. These theories and equations are used to design aircraft and have been for decades. If they didn't properly capture this behavior, we wouldn't be using them.

3. I'm not sure what you mean by 'sooner'. Flap deflection will decrease the stall speed. The points during the takeoff at which you rotate, begin climb, etc are based on airspeed. The angle of attack associated with that airspeed will vary based on flap deflection (and other things). I use 10 degrees of flaps in a single-engine Cessna to shorten my takeoff roll on short runways. More lift is produced at that flap setting, and the increase in drag is not enough to offset this benefit.